Systems and methods for over-the-air testing of wireless systems

ABSTRACT

Embodiments include systems and methods for over-the-air testing of wireless systems. Embodiments comprise separated anechoic chambers containing wireless devices. The anechoic chambers are connected by propagation path corridors.

PRIORITY

This application is a continuation of, and claims priority of, U.S.patent application Ser. No. 11/810,965, filed Jun. 7, 2007 now U.S. Pat.No. 7,965,968, which is incorporated herein by reference in itsentirety, and which is a non-provisional application that claimspriority of provisional U.S. Patent Application Ser. No. 60/811,679,filed Jun. 7, 2006.

FIELD

Embodiments are in the field of wireless communications. Moreparticularly, embodiments are in the field of over-the-air testing ofwireless systems.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the invention will become apparent upon reading the followingdetailed description and upon reference to the accompanying drawings inwhich like references may indicate similar elements:

FIG. 1 depicts a typical indoor multipath environment.

FIG. 2 depicts a typical indoor multipath environment with differenttest locations.

FIG. 3 depicts an indoor multipath environment with extraneousinterference.

FIG. 4 depicts a shielded room with excessive multipath.

FIG. 5 depicts multiple identical paths in a shielded room.

FIG. 6 depicts a fully anechoic chamber.

FIG. 7 depicts a semi-anechoic chamber.

FIG. 8 depicts an anechoic chamber with selectively placed absorbers.

FIG. 9 depicts a high Q shielded room with rotatable paddles(reverberation chamber).

FIG. 10 depicts a hybrid chamber with partially absorbing rotatingpaddles.

FIG. 10A depicts an alternative view of a selectively-linedreverberation room with MIMO antennas for connection to external testequipment.

FIG. 11 depicts separate anechoic chambers connected by a plurality ofpropagation path corridors.

FIG. 11A depicts a perspective view of two separated anechoic chambersconnected with parallel propagation path corridors.

FIG. 12 depicts separate anechoic chambers connected by waveguidesections.

FIG. 13 depicts separate anechoic chambers connected by corridorscomprising reflecting walls and absorbing baffles.

FIG. 14 depicts more than two separate anechoic chambers connected bypropagation path corridors.

FIG. 15 depicts multiple anechoic chambers connected by propagation pathcorridors with positioners to change the orientation of devices undertest (DUTs).

FIG. 16 depicts that any number of combinations of elements may beemployed for multi-corridor testing.

FIG. 17 depicts a lossy variable path chamber in connection withanechoic chambers through propagation path corridors.

FIG. 18 depicts propagation path corridors situated at angles in ananechoic chamber.

FIG. 19 depicts an alternative test using multiple antennas with avariable path simulator.

DETAILED DESCRIPTION OF EMBODIMENTS

The following is a detailed description of embodiments depicted in theaccompanying drawings. The embodiment(s) presented herein are merelyillustrative, and are not intended to limit the anticipated variationsof such embodiments; on the contrary, the intention is to cover allmodifications, equivalents, and alternatives falling within the scope ofthe appended claims. The detailed descriptions below are designed tomake such embodiments obvious to those of ordinary skill in the art.

Embodiments include systems and methods for over-the-air testing ofwireless systems. Some embodiments comprise separated anechoic chamberscontaining wireless devices. The anechoic chambers are connected bypropagation path corridors which provide multiple paths of differentpath lengths.

Multiple Input Multiple Output (MIMO) operation of devices compliantwith Institute of Electrical and Electronics Engineers (IEEE) standard802.11n requires a multipath environment to achieve the full benefit ofMIMO technology. For best results, a multipath test environment fortesting a MIMO system should be: isolated (shielded) from outsideinterference; repeatable from test to test; reproducible from test labto test lab; predictable with a standardized level of multipath; and arealistic model of multipath behavior in similar-to-real-worldenvironments. The choice of test environment can have a significanteffect on the resulting over-the-air test if all possible modes ofoperation are to be tested.

The 802.11n standard has defined a number of channel models for line ofsight (LOS) and non line of sight (NLOS) indoor and outdoorenvironments. Models include delay spreads of 15, 30, 50, 100, 140, 150and 250 nano-seconds (ns), corresponding to path lengths of 4.5, 9, 15,30, 42, 45, and 75 meters (m). Ideally, a MIMO test environment would beable to approximate one or more of these models to test the operation ofwireless devices. FIG. 1 shows a transmitting device 50 and a receivingdevice 51 in a typical indoor multipath environment illustratingpossible LOS and NLOS paths. FIG. 2 shows LOS and NLOS paths withdifferent test locations, resulting in different paths. FIG. 3 showsthat in a real world environment, the wireless system is also subject tounwanted extraneous interference from equipment 53.

FIG. 4 shows a result of using a shielded room (screen room) formultipath testing of a wireless system. The metal walls cause excessivemultipath propagation, far exceeding a number of paths found in a realworld setting. FIG. 5 shows that in a shielded room, symmetry causesmultiple identical paths that produce deeper fading than typically foundin the real world. Due to symmetry, signals reinforce each other in orout of phase. In a shielded room, energy bounces around until absorbedby other objects in the room or losses in the walls.

FIG. 6 shows a fully anechoic chamber with all boundaries covered withabsorber 70. This is unsuitable for multipath testing between multipleDUTs within that environment since no significant multipath remains,because of absorber 70. FIG. 7 shows a semi-anechoic chamber (usuallyused for Electromagnetic compatibility (EMC) testing) which leaves thefloor of the chamber reflective. In this setup, only one additional pathremains, and is thus unsuitable for realistic multipath testing. FIG. 8shows an anechoic chamber with selective positioning of absorber 70 tochoose specific multipaths. The multipaths so selected are dependentupon the position of the bare areas and long path lengths are difficultto achieve.

FIG. 9 shows a reverberation chamber comprising rotating paddles 61 in aHigh Q shielded room. The rotating paddles “stir” field modes forstatistical uniformity and result in variable multipath fading.

While several of the solutions described above could potentially beconfigured to produce the multipath behavior described by the 802.11nchannel models, each has its drawbacks. One problem is the overall sizerequired to produce a given path length without creating additionalsub-paths. A compact environment that's capable of generating long pathlength behavior is needed.

FIG. 10 shows a hybrid multipath chamber combining partially absorbingreflecting stir paddles 62 in a partial anechoic chamber. This testsetup provides more realistic variable multipath. FIG. 10A shows analternative view of a selectively lined reverberation chamber with MIMOantennas 63 for connection to external test equipment. Theconfigurations of FIGS. 10 and 10A can be described as low Q or lossyreverberation environments. Extreme multipath (slowly decaying RFsignals bouncing from walls and paddles) of these reverberation chambercan be made to look more like the real world by selectively loading thechamber until the desired decay profile is obtained.

Thus, some embodiments comprise an apparatus for over the air testing ofwireless devices, comprising a partially absorber-lined anechoicchamber, comprising: at least one wall that is only partially covered byabsorbing material. In some embodiments, the apparatus further comprisesa separate anechoic chamber connected to the partially lined chamberthrough a connecting propagation path corridor. In some embodiments, theapparatus further comprises a positionable stir paddle in the chamber.In some embodiments, the apparatus further comprises at least oneantenna within the chamber.

FIG. 11 shows an embodiment that combines separate anechoic chambers 101and 102 connected by propagation path corridors 103 that providepropagation paths of different lengths. Block 119 shows an edge viewindicating how the different propagation corridors can be stacked inparallel to provide multiple propagation paths simultaneously. FIG. 11Ashows a perspective view of two separated anechoic chambers 101, 102connected with the parallel propagation path corridors 119. Note thatalthough a rectangular geometry is shown. Other geometries, such as acircular-cylindrical geometry, may be employed. FIG. 12 shows samplepropagation path corridors connecting two separate anechoic chambers 101and 102. Each exemplary propagation path corridor may be a waveguide ofdifferent length. Thus, a first path length is provided by waveguide104, a second path length is provided by waveguide 105 and a third pathlength is provided by waveguide 106. These different propagation pathsmay be stacked or placed in parallel to provide multiple propagationpaths simultaneously. Each waveguide may be terminated with a suitablehorn antenna to direct the propagation as needed. Branches and shortedstubs can be used to create standing wave reflections of a desiredperiodicity. Note that instead of waveguide, other propagationmechanisms, such as coaxial cable, can be employed as propagation pathcorridors.

FIG. 13 shows two separate anechoic chambers 101 and 102 connectedthrough propagation path corridors 107, 108 and 109 constructed ofsuitable RF reflecting material. Absorbing baffles 110, 111, and 112 areplaced as needed to block unwanted paths and to select desired paths.Again, these different propagation paths may be stacked in parallel toprovide multiple propagation paths simultaneously.

FIG. 14 show that more than two separated anechoic chambers withabsorbers 70 can be connected through propagation corridors as describedabove to test more than two devices or sets of devices simultaneously inthe presence of multiple paths between them. Accordingly, in the exampleof FIG. 14, one anechoic chamber contains a transmitting device 50;another anechoic chamber contains a receiving device 51; anotheranechoic chamber contains a transmitting device 54; and another anechoicchamber contains a receiving device 55. FIG. 15 shows multiple anechoicchambers connected by propagation path corridors, with devices undertest mounted upon positioners 71 such as turntables that rotate.Movement of the positioners allows for statistical variation of thefields.

FIG. 16 shows anechoic chambers connected by propagation corridors withdifferent types of elements in each chamber. Thus, one chamber 72 is ofthe type shown in FIG. 10. Another chamber 74 is of the type shown inFIG. 7 and contains a stationary DUT. Another chamber 76 contains a DUTon a positioner. Another chamber 78 shows MIMO antennas that areconnected to external test equipment. Thus any combination of chambertypes and elements may be employed using propagation path corridors toconnect the chambers.

FIG. 17 shows an adjustable environment such a lossy reverberationchamber with paddles connected by propagation path corridors to twoseparate anechoic chambers containing a DUT and MIMO antennas. FIG. 18shows propagation path corridors arranged around the perimeter of achamber so that different delayed signals arrive from differentdirections. FIG. 19 shows an array of antennas surrounding a DUT in alossy chamber. Each antenna is connected to a variable path simulator tosimulate different propagation paths.

Thus, some embodiments comprise a test apparatus for over-the-airtesting of wireless devices. One embodiment comprises a plurality ofanechoic chambers, at least one chamber to contain a device under test;and at least one propagation path corridor connecting two or morechambers. In some embodiments, at least one propagation path corridor isa section of waveguide. In some embodiments, at least one propagationpath corridor comprises at least one absorbing baffle to selectivelypass a propagation path. In some embodiments, a plurality of propagationpath corridors provide a plurality of propagation paths of differentlengths. In some embodiments at least one chamber comprises a moveablepositioner on which a device under test can be mounted. In someembodiments, at least one anechoic chamber contains one or more antennasconnected to external equipment. In some embodiments, at least oneanechoic chamber exhibits at least one wall that is only partiallycovered by absorbers. In some embodiments, at least one anechoic chambercomprises at least one positionable stir paddle. Another embodimentcomprises: an apparatus for over the air testing of wireless devices,comprising an anechoic chamber; and an array of antennas connected to avariable path simulator. In some embodiments, the apparatus furthercomprises at least a second anechoic chamber connected through apropagation corridor to the anechoic chamber containing the antennas.

Thus, there are a wide range of alternatives to developing multipathbehaviors in a test environment suitable for 802.11n MIMO over-the-airtesting. A controlled test environment is preferable to unrepeatablereal world environments. Existing technologies such as shielded rooms oranechoic chambers in their typical configurations do not provide anideal solution. Thus, the new concepts provided herein provide moresuitable solutions for over-the-air testing of these systems.

The present invention and some of its advantages have been described indetail for some embodiments. It should be understood that variouschanges, substitutions and alterations can be made herein withoutdeparting from the spirit and scope of the invention as defined by theappended claims. An embodiment of the invention may achieve multipleobjectives, but not every embodiment falling within the scope of theattached claims will achieve every objective. Moreover, the scope of thepresent application is not intended to be limited to the particularembodiments of the process, machine, manufacture, composition of matter,means, methods and steps described in the specification. One of ordinaryskill in the art will readily appreciate from the disclosure of thepresent invention that processes, machines, manufacture, compositions ofmatter, means, methods, or steps, presently existing or later to bedeveloped are equivalent to, and fall within the scope of, what isclaimed. Accordingly, the appended claims are intended to include withintheir scope such processes, machines, manufacture, compositions ofmatter, means, methods, or steps.

1. A test apparatus for testing a wireless device in a multi-pathenvironment, the test apparatus comprising: a first partially linedreverberation chamber comprising surfaces that are lined with absorberand comprising reflecting surfaces that are not lined with absorber;within the first partially lined reverberation chamber, at least a firstrotatable obstacle that when rotated varies a multi-path effect of thetest apparatus; a second chamber coupled to the first partially linedreverberation chamber by a plurality of propagation path corridors; anda third chamber coupled to the first partially lined reverberationchamber by a plurality of propagation path corridors.
 2. The testapparatus of claim 1, wherein the rotatable obstacle is at leastpartially reflecting.
 3. The test apparatus of claim 1, wherein therotatable obstacle is at least partially covered with absorber.
 4. Thetest apparatus of claim 1, further comprising a second rotatableobstacle that when rotated varies a multi-path effect of the chamber. 5.The test apparatus of claim 1, wherein the second chamber exhibits arotating absorbing baffle.
 6. Test apparatus of claim 1, wherein thesecond chamber is adapted to hold a device under test and the thirdchamber is adapted to hold one or more antennas.
 7. A method of testinga wireless device in a multipath environment, the method comprising:providing a first partially lined reverberation chamber that includessurfaces that are lined with absorber and reflecting surfaces that arenot fined with absorber; providing a rotatable obstacle within the firstpartially aligned reverberation chamber that when rotated varies thevariable multipath environment to simulate a variable multipathenvironment; providing a second chamber coupled to the first partiallylined reverberation chamber by a plurality of propagation pathcorridors; and providing a third chamber coupled to the first partiallylined reverberation chamber by a plurality of propagation pathcorridors.
 8. The method of claim 7, further comprising selectivelylining, between tests, surfaces of the first partially linereverberation chamber to achieve a desired multipath effect.
 9. Themethod of claim 8, further comprising rotating the rotatable obstacle toachieve a desired multipath effect.
 10. The method of claim 7, furthercomprising rotating the rotatable obstacle to achieve a desiredmultipath effect.
 11. The method of claim 7, further comprisingproviding an additional one or more rotating obstacles.
 12. The methodof claim 11, wherein at least one of the rotating obstacles exhibits areflecting surface.
 13. The method of claim 7, wherein the rotatingobstacle exhibits a corner.
 14. A test structure, comprising: a firstpartially lined reverberation chamber having at least one rotatableobstacle; a second chamber adapted to hold a device under test, thesecond chamber coupled to the first partially lined reverberationchamber by a first set of propagation path corridors; and a thirdchamber adapted to hold at least one antenna, the third chamber coupledto the first partially lined reverberation chamber by a second set ofpropagation path corridors.
 15. The test structure of claim 14, whereinthe first partially lined reverberation chamber has a plurality ofrotatable obstacles.
 16. The test structure of claim 15, wherein aplurality of rotatable obstacles are positioned to achieve a desiredmulti-path effect.
 17. The test structure of claim 14, wherein the firstset of propagation path corridors is a plurality of waveguides ofdifferent electrical lengths.
 18. The test structure of claim 14,wherein the second chamber is a partially lined reverberation chamber.19. The test structure of claim 14, wherein the third chamber is apartially lined reverberation chamber.